The present invention relates to a method and apparatus for removing flash from a molded recorded disc, and more particularly to a method and apparatus for removing the flash so as to provide the disc with a smooth edge and a controlled diameter.
Recorded discs are flat circular plates of a plastic material having information on one or both surfaces thereof in the form of a surface relief pattern formed along a spiral path. The discs are generally formed in a mold press having a pair of mold plates, at least one of which is movable toward and away from the other and which, when together, form a mold cavity therebetween of the size and shape of the disc. On the opposed surfaces of the plates are stampers which have on their surfaces the negative of the surface relief pattern to be formed in the surfaces of the disc. When a disc is molded in such a mold press, excess plastic material flows radially outwardly beyond the edge of the mold cavity so that the molded disc has excess material around its edge, known as "flash," which must be removed. This removal of the flash is generally achieved by placing the still warm disc directly from the mold press onto a circular support plate so that the flash projects beyond the edge of the plate and rotating the plate. A knife is pressed against the rotating disc so that the knife cuts off the flash up to the edge of the disc. Such an apparatus is shown in U.S. Pat. No. 3,412,427 to J. Flusfeder et al., issued Nov. 26, 1968, entitled "Apparatus For Manufacturing Disc Records."
Recently there has been developed a high density recorded disc made of a plastic material which is filled with large amounts of conductive carbon. This type of disc is more brittle than discs which do not contain the conductive carbon. It has been found that when the flash is removed from this type of disc by means of a knife, the edge of the disc is not smooth. Also, since the disc is more difficult to cut with a knife, it is difficult to accurately control the diameter of the disc after flash removal. Since this type of disc is placed in a carrier or caddy to protect the surface of the disc from dirt and other contaminants, in order to permit the disc to be removed and replaced into the caddy, it is desirable to accurately control the diameter dimensions of the disc. Therefore, it is desirable to have means for removing the flash from the disc which provides the disc with a smooth edge and which will permit accurate control of the diameter of the disc.
A method and apparatus which has been developed to achieve this result includes a knife for removing the major portion of the flash which is referred to as the "bark," and a rotary cutter, such as a router, for making the final cut to the desired dimension of the disc. Such a method and apparatus is described in U.S. Pat. No. 4,326,325 to R. W. Chambers et al., issued Apr. 27, 1982, entitled "Method and Apparatus For Deflashing Molded Recorded Disc." Although this method and apparatus was found to be satisfactory, it does have some problems. The debris that is removed from the rotary cutter is in the form of fine particles. Although the apparatus includes suction means for removing the debris, the micro size particles are difficult to remove and have a tendency to get onto the disc. The particles on the disc can cause surface damage to the disc or clog up the fine dimension grooves in the disc. Also, the use of the rotary cutter requires additional equipment which adds to the expense of the apparatus used to make the disc. In addition, the rotary cutter and its drive motor contain materials, such as oils and lubricant, which can contaminate the disc surface. Finally, the rotary cutter still does not form an edge of the disc which is as smooth as is desired.